One-fifth of Booty to the Cause of Allah (Khumus)

Bukhari :: Book 4 :: Volume 53 :: Hadith 381

Narrated 'Abdullah bin Mughaffal:

While we were besieging the fort of Khaibar, a person threw a leather container containing fat, and I ran to take it, but when I turned I saw the Prophet (standing behind), so I felt embarrassed in front of him.